Press clutch, brake, and safety device inspection

⚙Care and inspection

• Check the pressure plate movement, stroke, and lining wearFriction clutch, disc brake

  Stop the slide at bottom dead center, stop the main motor, and operate the clutch (brake) several times in inching to watch the pressure plate movement. Measure the pressure plate stroke with a feeler gauge or similar, and check the lining for cracks and wear. If anything is abnormal, disassemble and inspect the friction plates, pressure plate, backing plate, hub, and springs

  As the lining wears the stroke grows, and the time to stop grows. When the clutch and brake deteriorate, the press cannot stop at the stopping performance set by the manufacturer and the safety distance becomes insufficient (example from MHLW risk reduction measures). Acceptance: the pressure plate moves smoothly and quickly, with no air leaks. Stroke and wear are appropriate in light of the machine's structure and performance (judged by the manufacturer's reference value). Where the lining is held by small screws, the screw heads are not worn (Specified Self-Inspection Standard). Use manufacturer-specified linings when replacing them (JFMA)^[1][2][3]

• Check the lining, drum, key, and tightening springShoe-type and band-type brakes

  Stop at bottom dead center and check the lining for cracks, wear, and oil. Measure scratches on the drum friction surface and play in the key that secures the drum (feeler gauge). Run one stroke and check the condition of the tightening spring

  When brake effectiveness falls, the stopping position shifts and the stopping time grows. Examples of acceptance: scratches on the drum are 1/3 or less of the total friction area with no severe scratches. Key play 0.2 mm or less. The spring coils are not touching and are adjusted correctly (Specified Self-Inspection Standard). Also, the brake of a newly built mechanical press must be something other than a band brake (Article 24 of the Structural Standard for Power Presses)^[1](1 source, for reference)

• Check solenoid valve operation and exhaust noise, and replace at end of lifeSolenoid valves for clutch and brake

  Stop the main motor, operate each valve in turn, and check that there is no visible abnormality or abnormal air supply/exhaust noise and that it operates reliably

  A solenoid valve fault leads to the clutch failing to release or the brake lagging. The Structural Standard requires a double, normally closed solenoid valve on mechanical presses controlled by air or hydraulics (Article 27). AIDA's guide for replacement or overhaul: clutch and brake solenoid valves, 5 years in continuous use and 3 years in single-stroke use^[4][1][5]

• Test that the overrun monitor worksOverrun monitor

  Delay the brake control time, for example by throttling or blocking the air port of the brake control solenoid valve, and watch the operation

  A device that stops the press quickly when it overshoots the stopping point. Crank presses running at 300 rpm or less, etc. must have one (Article 26 of the Structural Standard). Acceptance: it operates reliably when the stopping angle of the crankshaft etc. exceeds the set angle. For mechanical presses made on or after 1 July 2011, the slide must not move until it is returned to the start state by inching (Specified Self-Inspection Standard)^[1][4](1 source, for reference)

• Check that the rotation angle indicator matches the slide position and that the cam switch has no playRotation angle indicator, rotary cam switch

  Find the slide's bottom dead center with a dial indicator and compare it with the indicator reading. Check the drive of the rotary cam switch for play, wear, and looseness by hand-turning and coasting (chain tension if chain driven)

  Signals such as stopping position, overrun monitoring, and upstroke muting are determined by cam or encoder angle. If it drifts, the stopping position goes wrong. AIDA's replacement guide: rotary cam switch 3 years or 4 million cycles, encoder (incremental) 5 years^[1](1 source, for reference)

• Check the safety distance, protective height, and beam positionsLight curtain safety device

  Calculate the safety distance from the maximum stopping time and the continuous blocking width, and check that the measured distance between the beams and the danger limit is at least that (the calculation is a separate item). The vertical protective range is at least stroke length plus die height for mechanical presses, and at least daylight for hydraulic presses. The lowest beam is at the same height as the bolster top surface. If there is a gap between the beams and the front edge of the bolster where a hand can enter, provide a safety enclosure

  If the stopping time grows or the mounting position moves, the press can no longer stop before a hand reaches the danger limit. The Guideline considers a beam spacing of 75 mm or less appropriate. If the highest position of the slide bottom is 1,400 mm or less from the floor, the top of the protective range may be 1,400 mm, and if it exceeds 1,700 mm, 1,700 mm^[4][6][2][7]

• Check control spacing, simultaneous pressing, and single-stroke stopTwo-hand control (safe single-stroke type, two-hand start type)

  Test that it will not run unless the time difference between left and right is within 0.5 seconds, that releasing one hand on the closing stroke stops it quickly (safe single-stroke type), and that it cannot restart unless both hands are released after each stroke. Measure the distance (safety distance) between the controls and the danger limit

  If it can be operated with one hand, or with a time difference, it will run even with the other hand inside the die. The spacing between controls is 300 mm or more. With measures to prevent one-hand operation, 200 mm or more is also acceptable. A guard ring also prevents starting by a falling object (Guideline)^[4][6][8](1 source, for reference)

• Check sensor position, low closing speed, and hold-to-run controlLaser safety device for press brakes

  Install the sensor taking the inertia descent of the press brake into account, and adjust the beam position and the switching position to low speed with the dedicated test piece

  Because it shines a laser near the upper die and stops quickly when it detects a fingertip, it will not be in time unless stopping performance and mounting position match. It can be used only on press brakes whose slide speed can be set to 10 mm/s or less and which, at that speed, move only while the control is operated (Article 131, paragraph 2, item 3 of the Ordinance; in force July 2011). There is a case where two people worked without a safety device and a co-worker started the machine without checking, trapping an arm; MHLW also lists a two-person control device that closes only when both people press foot switches at the same time^{[6][9][10][7][11]}

• Minimize blanking (the function that disables some beams) and secure the additional distanceLight curtain with blanking

  Setting which beams to disable is done by a supervisor with a key switch. With fixed blanking, block both sides of the disabled part with fixed guards. With multi-beam interruption (floating blanking), the setting changes the continuous blocking width, so check the continuous blocking width on the nameplate and the additional distance

  A hand can enter through the disabled part. If switching the setting changes the continuous blocking width, the required safety distance changes too^[6][4](1 source, for reference)

• Check the safety block for damage and its interlock, and use it only for the correct workSafety block, safety plug, key lock

  Check the safety block (or slide-locking device) for breakage, deformation, chain damage, and loose mounting bolts, and test that the interlock that keeps the slide from moving while it is in use works

  When any part of the body enters the danger limit during die mounting, removal, or adjustment, workers must be made to use safety blocks, etc. to prevent unexpected slide descent (Article 131-2 of the Ordinance). There was a fatal case where a safety block used to release a workpiece from the die was struck by the upper die and flew, killing a worker (MHLW). Mechanical presses and press brakes whose bolster sides are each under 1,500 mm or whose die height is under 700 mm may use a safety plug or key lock instead (Article 31 of the Structural Standard)^{[9][4][1][12]}(1 source, for reference)

• Have the person designated keep the selector key, and check that it operates as the switch setting saysSelector key switch

  Check the key switch for play and bending, and test that it operates as marked in each selector position. The key is kept by the press work chief (the designated keeper at workplaces where none must be appointed)

  There was a case where the safety device was turned off and the key left in, and a worker trying to clear a material jam was caught by the slide (MHLW). Ordinance Article 134 item 3 and Article 134-2. For machines made on or after 1 July 2011, also check the function that prevents unintended continuous strokes (Specified Self-Inspection Standard)^[9][1][13](1 source, for reference)

• Inspect the slide suspension rod, springs, and air leaksCounterbalance

  Check slide suspension rods etc. for cracks and damage, springs for breakage, and for air leaks

  A pneumatic counterbalance must be built to stop the slide automatically if air pressure falls to the required pressure or below (Article 30 of the Structural Standard). Acceptance: no cracks or damage in the suspension rods, and no broken springs or significant air leaks (Specified Self-Inspection Standard)^[1][4](1 source, for reference)

• Check bolt looseness and function, and residual pressure during repairDie cushion

  Check bolts and nuts at each part for looseness, and the function and operation of the die cushion, its accessories, and piping

  There was a fatal case where, during repair of a die cushion that had stopped working, a shaft broke, the cushion pad jumped up, and the worker was caught between it and the upper die (MHLW). Before repair, confirm that the moving parts cannot move on residual pressure, and set safety blocks, etc. to prevent them from jumping up^[1][14](1 source, for reference)

• Check the amount of drop when stopped at the upper limit of work, and the automatic holding functionSlide drop prevention device, main operating valve

  Stop the slide at the upper limit of work and check how much it drops. For hydraulic presses made on or after 1 July 2011, check that the slide is held automatically so it does not descend under its own weight and is released when operated. If anything is abnormal, disassemble the main operating valve and check the spring and spring seat for fatigue

  Hydraulic presses must have a slide drop prevention device (Article 33 of the Structural Standard). The solenoid valve must be normally closed and spring return type (Article 34). The quick-stop time and the inertia descent (how far the slide drops before stopping) are also measured with a measuring device and a scale, and judged as appropriate or not for the machine's performance (Specified Self-Inspection Standard)^[1][4][8](1 source, for reference)

• Inspect the stopping brake and belt of the servo press, and the energy-storage capacitorsServo press brake, belt, and aluminum electrolytic capacitors

  Check the brake wear. For belt-coupled machines, check the belt for breakage and fatigue (Specified Self-Inspection Standard). For the capacitors, visually check for a bulging pressure valve and measure capacitance with an LCR meter (AIDA)

  A brake is needed to stop the slide if the servo system fails (Article 32 of the Structural Standard). When capacitors reach end of life, work energy runs short, and the press may stop from overvoltage during deceleration or stopping (AIDA). AIDA recommends an annual inspection because capacitors have a limited life. Replace them with press-specific parts. A servo press without a mechanical friction brake cannot stop the slide when it fails, so make it no-hands-in-die with a safety enclosure etc. (Guideline)^{[15][4][1][6]}

• Replace life-limited electrical parts on a plan, by the guide years or cyclesElectrical parts (motors, relays, magnetic contactors, switches, encoders)

  Keep the replacement guide (table) in a ledger and replace before the recommended replacement interval runs out. Replace relays, switches, motors, solenoid valves, and emergency stop buttons with manufacturer-specified parts

  Electrical parts cause sudden stops when they reach end of life. JFMA asks that manufacturer-specified parts always be used when replacing electrical and mechanical parts. AIDA's guide assumes that the maintenance and periodic inspection in the manual are carried out, and varies with the operating environment^[5][16][3]

• Keep long-lead-time, short-life, and consumable parts as spares, and know the lead time and price of parts you do not stockSpare parts

  Stock long-lead-time parts such as ball screws and bearings, short-life parts such as packings and electrical parts, and consumables such as linings and filters. For parts you do not stock, note the lead time, approximate cost, where used, and quantity

  Made-to-order parts such as medium to large motors take time to obtain, and the line can be down for a long time (AIDA). The suffix of a model number may indicate a special order, so check model numbers carefully^[16][17][3]

÷Safety distance calculation (safety presses and safety devices, light curtain and two-hand control types)

1. Read the maximum stopping time Tl + Ts (milliseconds) from the press nameplate (or the measured stopping performance). First check that the measured value is within the manufacturer's specified value
2. For a light curtain, read the additional distance C from the table using the continuous blocking width on the safety device nameplate (two-hand control has no C)
3. Safety distance D (mm) = 1.6 × (Tl + Ts) + C
4. Check that the measured distance between the beams (or the two-hand controls) and the danger limit is D or more

Light curtain

D = 1.6 × (Tl + Ts) + C [D: mm, Tl: time in ms from the hand blocking the beam until the quick-stop mechanism starts to work, Ts: time in ms from the quick-stop mechanism starting to work until the slide stops, C: additional distance in mm]

Two-hand control (safe single-stroke type)

D = 1.6 × (Tl + Ts) [Tl: time in ms from the hands leaving the controls until the quick-stop mechanism starts to work]

Meaning of 1.6

Hand speed of 1.6 m/s (= 1.6 mm/ms). The distance the hand moves during the time to stop (example from MHLW risk reduction measures)

Worked example: conditions

Maximum stopping time Tl + Ts = 150 ms, light curtain with continuous blocking width of 40 mm (additional distance 300 mm)

Worked example: result

D = 1.6 × 150 + 300 = 540 mm. With a device whose continuous blocking width is 30 mm or less, 240 mm (trial calculation)

If the clutch and brake deteriorate and the stopping time grows, the required safety distance grows too. Service the press to bring it back to its original stopping time (MHLW). The safety distance of a two-hand start type (a press without a quick-stop mechanism) is determined from the "required maximum time," but the formula could not be confirmed in the public materials this time^[4][6][2][7]

▦Additional distance C by continuous blocking width (Articles 43 and 45 of the Structural Standard for Power Presses)

The continuous blocking width is the smallest rod diameter that can be detected when a test rod is placed. A light curtain must be 50 mm or less, and a light curtain with control function 30 mm or less. The table in the Guideline writes the additional distance as "or more"^[4][6](1 source, for reference)

▦Wear and play limits for pin clutches, key clutches, and brakes (Specified Self-Inspection Standard for Power Presses)

Columns are the press capacity. R is the radius in mm on the R gauge. Older presses with pin clutches or key clutches (positive clutch presses) were in principle banned from manufacture by the 2011 revision of the Structural Standard (MHLW revision materials), but existing machines are still in use^[1][8](1 source, for reference)

÷Judging lateral runout of the flywheel (main gear) (Specified Self-Inspection Standard for Power Presses)

1. Run it, and if there is abnormal noise, lateral runout, or abnormal heating, measure the amount of lateral runout
2. Record the distance r (mm) from the measured position to the rotation axis and the measured lateral runout δ (mm)
3. Converted value a = δ ÷ r × 500 (runout converted to a position at a radius of 500 mm)
4. a ≤ 1 mm for plain bearings, a ≤ 0.5 mm for rolling bearings

Converted value

a (mm) = measured lateral runout (mm) ÷ distance from the measurement position to the rotation axis (mm) × 500

Worked example: conditions

Lateral runout 0.4 mm at a position 300 mm from the rotation axis, rolling bearing

Worked example: result

a = 0.4 ÷ 300 × 500 ≈ 0.67 mm, which exceeds 0.5 mm (trial calculation)

Per Figure 1 of the standard. If there is a main gear, measure the main gear^[1](1 source, for reference)

▦Guide for replacing or overhauling electrical parts (AIDA Engineering)

Conditional on carrying out the maintenance and periodic inspection in the manual, and varies with the operating environment. As reference, AIDA cites the Japan Electrical Manufacturers' Association (JEMA) recommendations for periodic inspection of general-purpose inverters and general-purpose PLCs^[5](1 source, for reference)