JUNE 1998

Ensuring consistent bolt torque

Problem: It's troublesome to get the consistent torque on engine cylinder head bolts to ensure secure connections. If they are installed loosely, leaks can occur; if they are too tight, they can be hard to remove for repairs.

Solution: This suggestion comes all the way from Holland, where DAF Trucks of Belgium found the solution to this problem. It turned to a Dutch lubrication distributor, Mavom BV, for help.

Experiments were conducted with special lubricants to reduce the coefficient of friction and the torque required to tighten the bolts. The lubricant selected in this case was Dow Corning 321 Dry Film Lubricant.

For bolt installation, it reduced the variation in coefficients of friction from +/-20 to +/-10, enough to double protection against cylinder head leaks. It also eased bolt removal for engine repairs.

As a result, the company coats all its truck cylinder head bolts with the lubricant to make bolt connections more predictable and maintenance easier.

Mr. O, the Practical Problem Solver, thanks Dow Corning Canada Inc., Mississauga, Ont., for this tip, which is adapted from the company's publication Materials News.

Solving conveyor chain shock problems in a pneumatic system

Problem: A sheet metal finishing company was having problems with a pneumatic, reversing pick and place system. The motor drove a linear trolley back and forth as it picked up sheets of steel from a pallet, carried them to the conveyor, and placed them in position for the finishing process.

The linear travel involved long strands of roller chain, which would whip badly at starting and stopping. Sometimes, the shock at start or stop would cause the chain to jump off the idler sprockets and the steel sheets would fall from the trolley. Control of the solenoid valves was through a PLC.

Solution: To correct these problems, the air motors were replaced with AC electric motors. An AC variable frequency inverter was installed along with some limit switches. These were all tied into the existing PLC, which provided the forward/reverse and start/stop commands.

The inverter provided a soft start and soft stop, eliminating the system shock while allowing increased production speeds.

Also, the roller chain and sprockets were replaced with open-ended urethane timing belts and sprockets. They do not require lubrication and they helped to reduce plant noise due to their quiet operation.

The pneumatic motors, which needed huge volumes of clean air, also were a continual maintenance problem. The new AC squirrel cage induction motors eliminated the need for the high volumes of air, and also operated quietly.

The PLC was reprogrammed to include new limit switches, which replaced the pneumatic shock absorbers. The changeover took two days to complete.

This case history was provided to Mr. O, the Practical Problem Solver, by Dave Strutt of BGS Bearings, Mississauga, Ont.