---
title: "Tie bar bushings and liner bushings"
url: "https://www.imspares.com/injection-molding-machine-parts/tie-bars/tie-bar-bushings/"
---

# Tie bar bushings and liner bushings

How tie bar bushings and liner bushings guide the platens of an injection molding machine, bronze and self-lubricating types, wear signs, and replacement.

A tie bar bushing is the bronze or self-lubricating sleeve fitted in a platen bore where a tie bar passes through. In the moving platen, flanged tie bar bushings guide the platen along the four bars as the mold opens and closes, and keep it square to the stationary platen. Plain liner bushings line other platen bores, such as the rear platen bores in the drawing, so that the platen can move along the bar without wearing the bar or the cast iron. Bushings are meant to wear instead of the tie bars, and replacing them in time protects the bars, the mold and the clamping accuracy.

## Where the bushings sit

- **Moving platen:** a flanged [tie bar bushing](https://www.imspares.com/parts/mc-tc-07/) at each face of the four bores. The moving platen travels the full opening stroke on every cycle, so these bushings do most of the sliding and wear the most.
- **Rear platen:** [liner bushings](https://www.imspares.com/parts/mc-tc-03/) in the bores. The rear platen moves along the bars only when the mold height is adjusted, so its liners wear slowly.
- **Stationary platen:** the tie bars are held in the stationary platen by their nuts and do not slide there. Whether its bores are lined depends on the design.

The tie bar bushings are not the same as the [toggle bushings](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-bushings/), which sit in the toggle link bores where the links turn on their pins.

## How tie bar bushings work

The bushing is a plain bearing. The bar is hard, ground steel and the bushing is softer bronze, so the wear happens in the cheaper, replaceable part. A film of grease or oil, fed through a grease nipple or the central lubrication system into grooves in the bushing, separates the two surfaces. Self-lubricating bushings carry a solid lubricant, often graphite plugs set into the bronze, and need little or no added lubrication, depending on the design.

On many machines the bushings also carry weight: the moving platen, the moving mold half and the ejector hang partly or fully on the tie bars. Many machines, especially larger ones, also support the moving platen on the machine frame, with slide shoes or a linear guide, so the bushings mainly guide. Either way the load is highest at the bottom of each bore, so that is where wear shows first.

## Types

| | Bronze bushing | Self-lubricating bushing |
|---|---|---|
| Material | Tin bronze, such as ZCuSn10P1 | Bronze with an embedded solid lubricant |
| Lubrication | Grease or oil through grooves, at the intervals in the manual | Little or none, depending on the design |
| Suited to | Machines with a reliable lubrication system | Points that are hard to lubricate or must stay clean |

Bushings are also made **flanged** or **plain**. The flange locates the bushing in the bore and is often bolted to the platen face. Our tie bar bushings are listed in tin bronze or self-lubricating versions, flanged or plain.

## Signs of worn tie bar bushings

- The moving platen drops at its mold face, or rocks when you push it with a bar while the mold is open.
- Bronze-colored smears, dark lines or score marks on the tie bars where the platen slides.
- The mold's guide pins and bushings wear quickly, or the mold halves knock as they meet.
- Flash or mismatch on one side of the part, and a [platen parallelism](https://www.imspares.com/injection-molding-machine-parts/platens/platen-parallelism/) error.
- Squealing or a dry sound as the platen moves, and black or gritty grease at the ends of the bushings.

Typical causes are missed lubrication, blocked grease lines, dirt or grit carried in on the bars, heavy molds hanging on the moving platen, a worn or badly adjusted platen support, and wear in the toggle that pushes the platen off line.

## Measuring bushing wear

1. Open the mold or remove it, then switch off and lock out the machine.
2. Set a dial indicator on a magnetic base on the machine frame, touching the top of the moving platen near one bore.
3. Lift the platen gently with a jack or a lever under it and read how far it rises. This is the vertical clearance in the bushings at that corner. Repeat at each bore.
4. When a bushing is out, measure its bore and the bar diameter at several points along the bushing's travel, in two directions at right angles, to find ovality and any wear on the bar.
5. Compare the readings with the limits in the machine manual or the manufacturer's data.

Record the readings each time: a slow increase over the months tells you when to plan the replacement.

## Replacing tie bar bushings

1. Remove the mold, switch off and lock out the machine, then support the moving platen securely, with lifting gear or blocks, so its weight is off the bushings.
2. Remove the flange screws or retainers and pull the old bushing out with a puller. Do not hammer it out against the bar.
3. Clean the bore, remove any burrs and check it for damage or ovality.
4. Line up the grease holes and grooves of the new bushing with the lubrication drillings in the platen, then press it in square. Some designs are an interference fit: follow the manual for the fit and the fitting method.
5. Lubricate, lower the platen, check that it slides freely over the full stroke, and measure parallelism.

Replace all the bushings of the platen together so they share the load evenly. If the bars are scored or worn, our [tie bar maintenance and replacement guide](https://www.imspares.com/blog/tie-bar-maintenance-replacement-guide/) explains how to judge whether they need replacing too.

## What to send for a replacement quote

Send the machine brand, model and serial number; the bushing's bore diameter (the tie bar diameter), outside diameter and length; the flange diameter, thickness and bolt holes; the position of grease holes and grooves; and whether you want bronze or self-lubricating. Photos of the old bushing with a caliper in view help. [Request a quote](https://www.imspares.com/request-quote/), and see the [tie bars guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/) for how the bushings fit with the rest of the assembly.

## Questions

### What is a tie bar bushing?

A tie bar bushing is a bronze or self-lubricating sleeve in a platen bore of an injection molding machine. It lets the platen slide along the tie bar and wears in place of the bar.

### What is the difference between a tie bar bushing and a liner bushing?

Tie bar bushings are the flanged guide bushings in the moving platen, which slides along the bars on every cycle. Liner bushings are plain sleeves that line other platen bores, such as the rear platen's, which moves along the bars only when the mold height is adjusted.

### How do I know if the tie bar bushings are worn?

The moving platen drops or rocks when pushed, the tie bars show score marks or bronze-colored smears, and the platens lose parallelism. Measure the clearance with a dial indicator while lifting the platen and compare it with the machine manual.

### Should all tie bar bushings be replaced at the same time?

Yes, replace all the bushings of a platen together. A new bushing next to worn ones takes more than its share of the load, and the platen still sits crooked.

## Replacement parts

- [MC-TC-03 Tie Bar Liner Bushing](https://www.imspares.com/parts/mc-tc-03/): Tie bar liner bushing for injection molding machine platen tie bar bores.
- [MC-TC-07 Tie Bar Bushing](https://www.imspares.com/parts/mc-tc-07/): Tie bar bronze bushing for injection molding machine platen guide bearings.